87 



olfactory in function. More probably it is some kind of 

 taste organ. Its function may be the testing' of the water 

 which enters the branchial cavity. 



The Auditory Organ. 



Eledone has one pair of statocysts, embedded in (he 



ventral wall of the cranial cartilage, and therefore just 

 below the sub-oesophageal nervous mass, between the 

 pedal and visceral ganglia. The membranous statocyst is 

 spherical, with a diameter of 6 mm., and lies in a 

 spherical cavity of somewhat larger dimensions. The 

 organ is attached to its cartilaginous capsule by a network 

 of fine arterial vessels, running to the wall of (he vesicle 

 (PI. VIII, fig. 08, Aud.caps., Aud.ves.). The venous 

 blood collects in the cavity of the capsule, and thence 

 passes out to the anterior vena cava, along with the blood 

 from the eye. Dorsally the smooth cartilaginous vail is 

 pierced by the auditory nerve and artery. Internally a 

 thin wall separates the two capsular cavities. 



The Statocyst itself is a spherical transparent 

 structure, lined with a flattened epithelium. Its antero- 

 dorsal wall is thickened into an oval pad, whose internal 

 wall is covered with columnar cells, bearing numerous 

 short cilia (fig. 07, s. d.). Besides this sensory pad, there 

 is also a sensory ridge, which runs from the former round 

 the dorsal wall of the vesicle, then over the ventral, and 

 finally ends on the dorsal surface (fig. 07, s. v.). Between 

 these two sensory regions is a low conical ridge which 

 projects inwards from the wall of the vesicle (fig. 07, pr.). 



The auditory nerve originates in the cerebral 

 ganglion, runs downwards, and leaving the pedal enters 

 the statocyst dorsally, and bifurcates. One branch ends in 

 the pad, whereas the other supplies the ridge, which is 



